Especially in the media industry huge amount of digital production data are being produced. For example, every movie produced in the 4 k digital cinema format leads, conservatively calculated, to as much as at least 12.5 TByte, assuming a frame rate of 24 Hz and a color resolution of 16 bit for every of the three (RGB) color-channels. Since not only the final movie data are produced, but also some additional scenes and their variations, for the above estimation the average length of all the corresponding movie data is assumed to add up to a total duration of 180 min.
According to the Organization for Economic Co-operation and Development in the US about 700 cinema movies have been produced in 2005. Since there are 9 major studios in the US, each studio produces about 950 TByte of data each year. In this respect it needs to be emphasized that this value is based on a very conservative calculation. In praxis, there will be much more digital data generated by each of the studios, which needs to be archived.
The produced media data represent an important asset of a film studio. During the pre- and post-production phase the gathered and generated media data are generally stored on hard disk drives. Since typical hard disk drives only have a guaranteed life-span of about five years, it is not advisable to use hard disk drives for long archival of the data.
Unfortunately, there is today no really reliable long-term mass storage technology available at reasonable costs, which would allow to directly archive the produced digital data. All typically employed mass storage technologies, e.g. tapes, digital versatile disks (DVD) or Blu-ray disks (BD) as well as some less common optical storage disks, do not provide the necessary durability of several decades. As a result, these mass storage technologies require high maintenance costs since the stored data needs to be copied to new media before the end of the life-span of the storage media.
U.S. Pat. No. 6,151,287 discloses a mass optical memory having a photo-sensitive layer formed on an optical disc, which includes elementary cells distributed across its free surface, for recording data with a laser beam. For each elementary cell the optical memory comprises a light guiding rod operative as a single-mode optical fiber, made from a photo-sensitive material, the axis of which is approximately orthogonal to the free recording surface. The optical memory has an increased storage density, but is rather difficult to manufacture due to the complex structure that needs to be produced.
In the document S. Bian et al.: “Erasable holographic recording in photosensitive polymer optical fibers”, Appl. Opt. Vol. 28 (2003), pp. 929-931, it has been proposed to store data as holograms in special optical fibers. However, as the necessary polymer optical fibers, which are doped with dye material, are costly to manufacture and are only available with rather short lengths, this approach is not suitable for mass storage. Also, the holograms need to be illuminated along the fiber axis. Due to the absorption caused by the dye material, which amounts to ˜0.7 cm−1, propagation of the reading or recording light along the fiber is confined to a couple of centimeters.
In this regard US 2011/0141871 discloses a method and an apparatus for storing data in an optical fiber. The bulk of the fiber is irradiated with a powerful irradiation beam in order to modify a characteristic of the bulk for data storage. Modification of the bulk of the fiber ensures a reliable storage of the data for a long period. However, the achievable data density is rather small.